1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a printer, or a facsimile apparatus and, more particularly, to an image forming apparatus having a cleaning blade for cleaning a toner left on an image carrier belt of the image forming apparatus.
2. Description of the Related Art
In a conventional image forming apparatus such as a copying machine, a printer, or a facsimile apparatus, an arrangement having a transfer unit on the upper surface of the image carrier belt to transfer and form a toner image on the lower surface of a recording sheet has the following advantages because a sheet convey unit is arranged in an upper portion of the image forming apparatus. Removal of a jammed sheet upon jamming and replenishment of sheets can be advantageously simplified. A sheet can be exhausted while an image surface faces down, so that confidentiality can be advantageously ensured.
In an image forming apparatus of this type, a toner left on the image carrier belt after image transfer is preferably cleaned in a range of downward movement of the image carrier belt or a range corresponding to the lowermost position due to the following reason. When cleaning is performed at a position away from the transfer unit, i.e., in the range of upward movement of the image carrier belt, the interior of the apparatus is contaminated or proper layout of other process means such as a latent image forming means and a developing unit which are adversely influenced by toner contamination becomes difficult by toner particles removed from the belt in the range of upward movement of the image carrier belt.
However, when the image carrier belt is cleaned with a blade in the range of downward movement of the belt, the following problems occur. That is, when the cleaning blade is brought into contact with the image carrier belt, i.e., when contact angle a1 of blade 101 and image carrier belt 102 is less than 90.degree. (FIG. 1A) so that the blade direction is a counter direction of the feed direction of belt 102 (this contact state will be referred to as a "counter" contact state hereinafter), a reaction force of blade 101 acts to interfere movement of image carrier belt 102 in a direction of an arrow upon catching of toner 103 by blade 101. Image carrier belt 102 then slips on a drive roller to cause variations in speed of belt 102. Contact angle .alpha.2 between belt 102 and blade 101 must be larger than 90.degree. (FIG. 1B) so that the direction of blade 101 is the same as the feed direction of belt 102 (this contact state will be referred to as a "with" contact state hereinafter). Reference symbol 104 in FIGS. 1A and 1B denotes a belt support member.
When blade 101 is brought into contact with image carrier belt 102 in the "with" contact state in the range of downward movement of belt 102, toner 103 is accumulated between the image carrier surface of image carrier belt 102 and the blade contact portion. The accumulated toner pushes the blade upward to cause incomplete cleaning.